As people age, the onset of presbyopia (the deterioration of near vision due to loss of flexibility in the human lens) is virtually inevitable. Indeed, some estimates are that 90 million people in the United States either have it or will have it by 2014.
The problems associated with presbyopia are compounded by the expanding use of personal computers, wherein users often view objects in three primary ranges: near for keyboards and papers (approximately 13 to 16 inches); intermediate for the computer monitor's screen and other intermediate ranged objects (approximately 16 to 72 inches); and distance (beyond approximately 72 inches) for objects beyond the intermediate range. These ranges are examples only, and vary depending on the severity of the presbyopia and the preference of the user.
Observers have recognized that, because of presbyopia, there is a need for eyeglasses that are tailored for use with computers. Such glasses are often referred to as computer glasses or computer lenses. In particular, it is recognized that users will benefit from lenses that correct for presbyopia with a near vision magnifying segment, an intermediate vision magnifying segment, and a distance segment. Similarly, lenses have been used that include only near and intermediate vision magnifying segments. In the latter case, for distance viewing, users either take off the glasses or peer over the top of the glasses.
Unfortunately, these computer lenses and glasses are relatively expensive, because, among other things, they are made from relatively thick lens blanks (often approximately 9 millimeters thick before grinding), and must be ground down to the proper magnifications. Also, these thick lens blanks are available only in quarter magnifying power increments, and thus are unsuitable for users who have needs that do not fit into those quarter increments. For example, with people in the age range of about 40-50 years, a very desirable power ratio for intermediate/near viewing with computers is approximately 1:2. Thus, if lenses are desired with a near power of 1.75, then an intermediate power of 0.875 is needed, which combination cannot be made with such lenses. As another example, with people in the age range of about 50-60 years, a very desirable power ratio for intermediate/near viewing with computers is approximately 2:3. Thus, if lenses are desired with a near power of 2.75, then an intermediate power of 1.82 is needed, which combination also cannot be made with such lenses.
Many inexpensive, over-the-counter glasses are also available for correcting the effects of presbyopia, and are often made from relatively thin lens blanks (less than approximately 5 millimeters thick). However, to the inventor's knowledge, these glasses either provide magnification for only one range, or, if they are bifocal, not for both near and intermediate ranges. Thus, they are generally not suitable for computer glasses.
Furthermore, to the inventor's knowledge, no “executive” lenses—those that have a line between the lower and upper segments of the lens, all the way across the lens—have been made with a reader power on the bottom and an intermediate power on the top.
Therefore, a need has arisen for eyeglasses and lenses that are made from thin lens blanks and which correct for the effects of presbyopia for both near and intermediate viewing.